This invention is concerned with the novel long-acting somatostatin analog, ##STR2## and the novel process for preparing said somatostatin analog. This invention encompasses the novel blocked .beta.-mercaptopropionyl-containing peptide intermediates, S-Acm-.beta.-mercaptopropionyl-(.epsilon.-INOC)Lys-Asn-Phe-Phe-Trp-(.epsil on.-INOC)Lys-Thr-Phe-Thr-Ser-(Acm)Cys-OH and S-Acm-.beta.-mercaptopropionyl-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-(Ac m)Cys-OH useful in the preparation of said analog. All the abbreviations used herein are defined below.
Somatostatin is a tetradecapeptide having the structure: ##STR3## and is known to inhibit the release of growth hormone. Somatostatin itself has a short duration of action because it is inactivated, inter alia, by aminopeptidases present in vivo. This problem of the short duration of action has been partially solved in the prior art by preparing derivatives of somatostatin which have low solubility, thus attaining a slow release on subcutaneous injection. Once dissolved, however, the derivatives are no more stable to hydrolysis by aminopeptidases than somatostatin itself. The present invention provides a somatostatin analog having the biological activity of somatostatin and a longer duration of action and a novel method for preparing said analog. The somatostatin analog of the present invention differs from somatostatin itself by virtue of the fact that the component Ala-Gly-Cys-OH in somatostatin is replaced by the .beta.-mercaptopropionyl group. This somatostatin analog, designated des(Ala.sup.1 -Gly.sup.2)desaminocys.sup.3 -somatostatin, has no .alpha.-amino group, thus eliminating one of the groups involved in enzymatic cleavage of the molecule. Therefore, this analog is resistant to cleavage in vivo by aminopeptidases and thus has a prolonged duration of action.
The abbreviated designations, which are used herein for the amino acid components, certain preferred protecting groups, amino acid activation groups, condensing agents, reagents and solvents employed in the process of this invention are as follows:
______________________________________ Abbreviated Designation Amino Acid ______________________________________ Lys L-lysine Asn L-asparagine Phe L-phenylalanine Trp L-tryptophan Thr L-threonine Ser L-serine Cys L-cysteine ______________________________________
______________________________________ Abbreviated Protecting Designation Groups ______________________________________ Acm acetamidomethyl INOC isonicotinyloxycarbonyl BOC tert-butyloxycarbonyl OMe methyl ester ______________________________________
______________________________________ Abbreviated Activating Designation Groups ______________________________________ NPE p-nitrophenyl ester HSE N-hydroxysuccinimide ester HBT 1-hydroxybenzotriazole ______________________________________
______________________________________ Abbreviated Condensing Designation Agents ______________________________________ DCCI dicyclohexylcarbodiimide ______________________________________
______________________________________ Abbreviated Designation Reagents ______________________________________ TFA trifluoroacetic acid TEA triethylamine DIPEA diisopropylethylamine DNTB 5,5'-dithiobis-(2- nitrobenzoic acid) ______________________________________
______________________________________ Abbreviated Designation Solvents ______________________________________ EPAW ethyl acetate-pyridine- acetate acid-water BAW butanol-acetic acid-water CMW chloroform-methanol-water DMF dimethylformamide THF tetrahydrofuran ______________________________________